On Ocbtober 1st, Facebook will require an SSL certificate for your site for when it's being displayed in a Canvas view or Page Tab (basically, anything from your site that's displayed within a Facebook.com page). The SSL requirement does not affect the login functionality, social buttons, or other features that are used on your site itself.
We have a guide on how to obtain an SSL certificate for as low as $17 for one year (or even like $10/year for multiple years), if interested in getting one:
Facebook SSL Certificates
Alex